A conventional bipolar battery generally includes electrodes having a metallic conductive substrate on which positive active material forms one surface and negative active material forms the opposite surface. The active materials are retained by various means on the metal conductive substrate which is nonconductive to electrolyte ions. The electrodes are arranged in parallel stacked relation to provide a multi-cell battery with electrolyte and separator plates that provide an interface between adjacent electrodes. Conventional mono-polar electrodes, used at the ends of the stack are electrically connected with the output terminals. Most bipolar batteries developed to date have used metallic substrates. Specifically, bipolar lead-acid systems have utilized lead and alloys of lead for this purpose. The use of lead alloys, such as antimony, gives strength to the substrate but causes increased corrosion and gassing.
In most known plates for bipolar batteries, the positive active material, usually in the form of a paste is applied to the metallic conductive substrate on one side while the negative active material is similarly applied to the opposite side. The plates may be contained by a frame which seals the electrolyte between plates so that it cannot migrate through the plate.
In U.S. Pat. No. 4,275,130, a bipolar battery construction 20 is disclosed having a plurality of conductive biplates 21. Each bipolar plate 21 may include a composite, substrate sheet 34 including a continuous phase resin material, which is nonconductive to electrolyte ions. The composite substrate sheet 34 also includes uniformly distributed, randomly dispersed conductive fibers 33 embedded in the material. The binder resin is a synthetic organic resin and may be thermosetting or thermoplastic. The composite substrate sheet 34 has substantially flat opposite side faces 35 which include at their surfaces exposure of portions of the embedded graphite fibers 33. The embedded graphite fibers not only provide electrical conductivity through the substrate sheet 34, but also impart to the thermoplastic material a high degree of stiffness, rigidity, strength and stability. Substrate sheet 34 may be made in any suitable manner such as by thoroughly intermixing the thermoplastic material in particle form with the graphite fibers. The mixture is heated in a mold and then pressure formed into a substrate sheet of selected size and thickness. After the sheet has been cured, the substantially flat side faces 35 may be readily treated or processed, as for example by buffing, to eliminate pinholes or other irregularities in the side faces.
As disclosed, lead stripes are bonded to the composite substrate sheet 34 by known plating processes. On the positive side face 35, the facial areas between lead stripes 38 are covered by a coating of corrosion resistant resin 36 suitably a fluorocarbon resin such as Teflon (polytetrofluoroethylene) which protects against anodic corrosion of the adjacent graphite fibers and polyethylene of the substrate 34. On the negative side face 35, facial areas between lead stripes 37 may be protected by a thin coating of resin impermeable to electrolyte such as a polyethylene coating 36a. In fabrication of the bipolar plate 21 and after the composite substrate sheet 34 has been formed, a thin Teflon sheet may be bonded to the positive side surface 35. Prior to bonding, window like openings corresponding in length and width to the lead stripes are cut. Plating thereafter will bond the lead in stripes 38 to the exposed conductive graphite surfaces on the substrate side face 35. The same fabrication process may be utilized on the negative side face 35 to coat the nonstriped areas with polyethylene or other like material. Plating of the negative stripes may be achieved as with the positive stripes.
A separator plate 23 serves to support the positive active material 24 and the negative active material 25 and may be made of a suitable synthetic organic resin, preferably a thermoplastic material such as microporous polyethylene.
Battery construction 20 includes a plurality of conductive bipolar plates 21, peripheral borders or margins thereof being supported and carried in peripheral insulating casing members 22. Interleaved and arranged between bipolar plates 21 are a plurality of separator plates 23 The separator plates carry positive active material 24 on one side thereof and negative active material 25 on the opposite side thereof. The casing members 22, together with the bipolar plates 21 and separator plates 23, provide chambers 26 for containing electrolyte liquid. At each end of battery construction 20, standard bipolar plates 21 interface with current collecting plates, where 27 is the negative collector plate and 28 is the positive collector plate. Externally of end collectors 27 and 28 are provided pressure members 30 interconnected by rods 31 having threaded portions for drawing the pressure members plates together and applying axial compression to the stacked arrangement of bipolar plates and separator plates.
The bipolar plate 21 is lightweight, rigid, but includes joint lines between the lead stripe edges and protective coatings to resist corrosion and structural deterioration of the substrate. Furthermore, a plating process is required in order to bond the lead stripes 37, 38 to the conductive substrate having graphite fibers. Conductivity is limited by the size and amount type of graphite fibers in the substrate. Additionally, a plurality of bipolar plates 21 and layers are required to sit in separate casing members 22 and an external frame, all of which require further processing steps for more parts. The bipolar battery construction 20 is a complicated design having many layers of materials and substrates assembled in multiple chambers 26 and bodies 43 that are secured together by a complex external frame.